| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Spencer | 1 | 11,253 | 11,302 | 0.31% | 1,028 | 11 | City |
| Everly | 2 | 560 | 573 | -0.18% | 535 | 1 | City |
| Royal | 3 | 375 | 380 | 0% | 1,271 | 0 | City |
| Peterson | 4 | 313 | 319 | 0% | 603 | 1 | City |
| Fostoria | 5 | 227 | 234 | -0.44% | 559 | 0 | City |
| Dickens | 6 | 145 | 147 | 0% | 174 | 1 | City |
| Webb | 7 | 135 | 139 | 0% | 268 | 1 | City |
| Greenville | 8 | 65 | 66 | 0% | 392 | 0 | City |
| Rossie | 9 | 46 | 47 | 0% | 319 | 0 | City |
| Gillett Grove | 10 | 31 | 32 | 0% | 140 | 0 | City |
Spencer is the largest city in Clay County, with a population of 11,253.
Gillett Grove is the smallest city in Clay County, with a population of 31.
There are 10 cities in Clay County, Iowa.